Allergen immunotherapy is a treatment that retrains your immune system to tolerate substances that trigger allergic reactions, such as pollen, dust mites, pet dander, mold, or insect venom. Unlike antihistamines and nasal sprays that mask symptoms, immunotherapy targets the underlying cause of allergies. A full course typically takes three to five years, but the benefits can persist for years after treatment ends.
How Immunotherapy Changes Your Immune System
In allergic people, the immune system overreacts to harmless substances by producing a type of antibody called IgE, which triggers inflammation. Immunotherapy works by gradually exposing you to increasing amounts of the allergen, which shifts the immune response in several important ways.
The central change involves a type of immune cell called a regulatory T cell. Over time, repeated allergen exposure encourages your body to produce more of these cells, which act as peacekeepers. They suppress the overactive allergic response by dialing down the inflammatory signals that drive symptoms like sneezing, itching, and swelling. They also reduce the activity of mast cells, basophils, and eosinophils, the frontline cells responsible for allergic inflammation.
At the antibody level, regulatory T cells promote a shift away from IgE (the allergy antibody) toward IgG4, a non-inflammatory antibody that can intercept allergens before they trigger a reaction. This combination of suppressed inflammatory cells, reduced IgE, and increased blocking antibodies is what produces lasting tolerance rather than just temporary relief.
Shots vs. Tablets: Two Ways to Get Treatment
Immunotherapy comes in two main forms. Subcutaneous immunotherapy (SCIT) involves injections given in a doctor’s office. Sublingual immunotherapy (SLIT) uses tablets or drops placed under the tongue, which you can take at home after the first dose is supervised.
Allergy shots have been used for over a century and can be customized for a wide range of allergens, often combining several in one vial. The tradeoff is frequent office visits, especially during the early phase, and the discomfort of needles. Sublingual tablets avoid injections entirely and don’t require regular clinic trips, making them particularly appealing for children. However, SLIT tablets are currently available for only a limited set of allergens: grass pollen, ragweed, and dust mites.
The Treatment Timeline
For allergy shots, treatment happens in two phases. The buildup phase lasts three to six months, during which you receive injections with gradually increasing allergen doses, typically one to two times per week. Once you reach your target dose, you enter the maintenance phase, where injections are spaced to roughly once a month. This maintenance phase continues for three to five years.
Sublingual tablets follow a simpler schedule. You take a daily tablet at home, usually starting a few months before allergy season for seasonal allergens or year-round for dust mites. The total treatment duration is the same: three to five years for lasting benefit.
Completing at least three years is critical. Studies consistently show that stopping before three years is associated with symptom relapse within a year. But patients who complete a full three-year course maintain reduced symptoms for at least two to three years after stopping, and some studies have tracked benefits lasting even longer. In one trial, symptom scores remained 25 to 36% lower than placebo across five consecutive pollen seasons, including two years after treatment ended.
How Well It Works
For allergic asthma, the results are striking when treatment is sustained. In one real-world study, 96.3% of patients who completed three years of immunotherapy were able to reduce or completely stop their inhaled corticosteroids while maintaining asthma control. By comparison, only about half of untreated patients achieved the same result. After three years, 63% of the immunotherapy group had stopped their inhaled steroids entirely, versus just 9.3% in the comparison group.
Asthma flare-ups also dropped significantly. During the first year, only 8.3% of immunotherapy patients experienced an acute episode, compared to 27.9% of those on standard treatment alone.
For insect venom allergies, immunotherapy is especially effective and can be lifesaving. Treatment prevents severe sting reactions in 91 to 96% of people allergic to wasp venom and 77 to 84% of those allergic to honeybee venom.
Starting Early in Children
One of immunotherapy’s most compelling benefits in children is its potential to prevent allergies from progressing. Children with hay fever are at elevated risk of developing asthma later, a pattern known as the allergic march. Immunotherapy can interrupt this progression.
Modeling studies show that starting sublingual tablets at age 5 results in only 19% of children developing allergic asthma over 20 years. Waiting until age 7 raises that figure to 24%, and starting at age 12 pushes it to 29%. The earlier treatment begins, the greater the long-term protection. There is no universally fixed minimum age, but sublingual tablets have been studied in children as young as five, and allergy shots are generally considered appropriate from around the same age depending on the child’s ability to cooperate and communicate symptoms.
Side Effects and Safety
Local reactions are the most common side effect for both forms. With allergy shots, 26 to 86% of patients experience redness, swelling, or itching at the injection site. With sublingual tablets, about 79 to 84% of patients report mild mouth or throat irritation, oral itching, or slight swelling, particularly in the first few weeks. These local reactions are generally mild and tend to diminish over time.
Systemic reactions (symptoms beyond the injection or application site) are uncommon with shots, occurring at a rate of about 0.1 to 0.2% of injection visits. Severe, life-threatening reactions are rarer still: roughly one per 100,000 injection visits. This is why allergy shots are given in a medical office, and you’re asked to wait 20 to 30 minutes afterward for observation.
Sublingual immunotherapy carries an even lower risk of serious reactions. Out of an estimated one billion SLIT doses administered worldwide since 2000, only 11 cases of non-fatal anaphylaxis have been documented. About 2.7 reactions occur per 1,000 doses overall, and only 0.056% of those are classified as severe.
Who Should and Shouldn’t Get It
Immunotherapy is recommended for people with confirmed allergic rhinitis, allergic asthma, or insect venom allergy whose symptoms aren’t well controlled by avoidance measures and medications, or who want to reduce long-term medication use. An allergist confirms the specific triggers through skin prick testing or blood tests before designing a treatment plan.
Several situations make immunotherapy inappropriate. Starting treatment during pregnancy is not recommended, though women who become pregnant while already on maintenance can typically continue. Active, uncontrolled asthma is a temporary contraindication, as are acute infections and febrile illnesses. A history of severe anaphylaxis from a prior immunotherapy dose is generally a reason to stop. For sublingual therapy specifically, active mouth sores, recent dental surgery, or oral infections are reasons to pause temporarily.
Patients taking certain heart and blood pressure medications (beta-blockers and ACE inhibitors) were historically excluded, but recent guidelines have softened this stance. Current recommendations suggest immunotherapy can be considered for these patients through shared decision-making with their allergist, particularly for those already on a stable maintenance dose.
What the Experience Looks Like
If you opt for shots, expect weekly or biweekly office visits during the buildup phase, each taking about 30 to 45 minutes including the observation period. Once you reach maintenance, visits drop to once a month. Many people schedule these around work or school and find the routine manageable, though the time commitment over several years is real.
Sublingual tablets fit more easily into daily life. After your first dose is taken under medical supervision, you place a tablet under your tongue each morning at home. It dissolves in about a minute. Most people experience the mouth tingling and itching mainly in the first few weeks, after which it fades or becomes barely noticeable.
The symptom improvement isn’t instant. Most patients begin noticing meaningful relief within the first several months, with benefits continuing to build over the first one to two years. The full effect of treatment, including the lasting immune changes that persist after stopping, requires completing the full three-to-five-year course.